env.d.2/fra/2012/2005: impacts of noise and use of...

Cefas contract report: C6082

ENV.D.2/FRA/2012/2005:

Impacts of noise and use of

propagation models to predict

the recipient side of noise

Final Report

Authors: J.F. Borsani, R. Faulkner, N.D. Merchant

Issue date: May 2015

Impacts of noise and use of propagation models to predict the recipient side of noise i

Cefas Document Control

Title: ENV.D.2/FRA/2012/0025: Impacts of noise and use of

propagation models to predict the recipient side of noise

Final Report

Submitted to: Lydia Martin-Roumegas

Date submitted: 29/05/2015

Project Manager: Kelly Baker

Report compiled by: J. Fabrizio Borsani, Rebecca Faulkner, Nathan D. Merchant

Quality control by: Kelly Baker

Approved by & date: John Bacon

Version: 1.4

Version Control History

Author Date Comment Version

J.F. Borsani 15/09/2014 Initial draft 1

M. Tasker 21/09/2014 Review

J.F. Borsani & R.

Faulkner

24/09/2014 M.Tasker comments

addressed

1.1

J.F. Borsani & R.

Faulkner

27/10/2014 Revised version 1.2

K. Baker 12/3/2015 Formatting edits 1.3

N.D. Merchant 28/5/2015 Final version 1.4

Impacts of noise and use of propagation models to predict the recipient side of noise ii

Impacts of noise and use of propagation models to predict the recipient side of noise iii

ENV.D.2/FRA/2012/0025: Impacts of noise and use of

propagation models to predict the recipient side of noise

Final Report

Authors: J.F. Borsani, R. Faulkner, N.D. Merchant

Issue date: May 2015

This report can be cited as:

Cefas (2015). Impacts of noise and use of propagation models to predict the recipient side of noise.

Report prepared under contract ENV.D.2/FRA/2012/0025 for the European Commission. Centre for

Environment, Fisheries & Aquaculture Science, UK.

Head office

Centre for Environment, Fisheries & Aquaculture Science

Pakefield Road, Lowestoft, Suffolk NR33 0HT, UK

Tel +44 (0) 1502 56 2244 Fax +44 (0) 1502 51 3865

www.cefas.defra.gov.uk

Cefas is an executive agency of Defra

Impacts of noise and use of propagation models to predict the recipient side of noise iv

Impacts of noise and use of propagation models to predict the recipient side of noise v

Table of contents

1 Introduction ................................................................................................................................... 1

2 Current knowledge gaps .............................................................................................................. 3

3 Legislation review ......................................................................................................................... 7

4 Review of underwater acoustic propagation models .............................................................. 10

5 Use of sound maps for assessing Indicator 11.2.1 ................................................................. 12

6 Outcomes of workshop on methodologies and guidelines .................................................... 14

7 Roadmap ...................................................................................................................................... 16

8 References ................................................................................................................................... 22

Impacts of noise and use of propagation models to predict the recipient side of noise Page 1 of 24

1 Introduction

Underwater noise pollution can have a range of adverse effects on marine biota. To address the risk

of negative ecological consequences, regulators and legislatures are beginning to take management

actions which will lead to evidence-based assessment of whether current levels of noise pollution are

harmful to the ecosystem as a whole. In 2010, the European Commission (EC) published two Indicators

for underwater noise (EC Decision 2010/477/EU) under Descriptor 11 of the Marine Strategy

Framework Directive (MSFD), which states that to attain Good Environmental Status (GES),

underwater noise should be “at levels that do not adversely affect the marine environment” (MSFD

2008/56/EC). These two Indicators are:

Indicator 11.1.1 for low- and mid-frequency impulsive sounds. These noise sources, such as

pile driving, seismic surveys, and explosions, have been associated with injury, displacement,

and behavioural disturbance of marine fauna.

Indicator 11.2.1 for continuous low frequency sound (ambient noise). Rising levels of ambient

noise, particularly from shipping, have been linked to masking of bioacoustic signals, chronic

stress, and developmental and behavioural effects.

It was considered that defining quantitative criteria for GES was difficult based on the current

knowledge of noise impacts on marine biota, and so initial Indicators were chosen to reflect the

environmental pressures, rather than the absolute status with respect to noise. This difficulty is

particularly the case for Indicator 11.2.1, where there are currently insufficient data to assess whether

absolute levels of background noise may have negative consequences for individual species.

Nevertheless, if long-term trends in noise levels are known then it may be possible to draw some

conclusions about changes in environmental pressures. For example, it was considered that a

downward trend in this Indicator was more likely to lead to GES than an upward trend. The EU

Technical Group on Underwater Noise (TG Noise) has suggested that trends alone are not sufficient

to describe GES, since trends do not indicate whether absolute levels of noise are harmful. However,

in the absence of an evidence-based threshold and as a precautionary approach, a downward trend

could be adopted as an interim target until further work is completed.


In the context of this uncertainty in the relationship between noise levels and environmental status,

the EC commissioned the present project (ENV.D.2/FRA/2012/0025: Impacts of noise and use of

propagation models to predict the recipient side of noise) with the following objectives:

1. To evaluate the current knowledge of the impacts of noise on marine biota at all levels

(individuals, populations, and ecosystems) and methods to assess these impacts.

2. To develop modelling techniques to predict the recipient side of noise, i.e. as it is received by

marine fauna.

Key elements of this work were to convene a workshop of international experts aimed at addressing

the current knowledge gaps, and to prepare a roadmap towards defining noise limits for GES.

This report summarises the outcomes of the project in non-technical language, drawing on the six

task-specific reports which are provided in the Supplementary Annexes for further information.

Chapter 2 presents an assessment of knowledge gaps in the effects of noise on marine biota, while

Chapter 3 briefly reviews current legislation and regulation relating to marine noise pollution. The

following two chapters address acoustic modelling: in Chapter 4, the main outcomes of a review of

acoustic propagation models are discussed, and Chapter 5 presents sound maps which were

developed for the project. The main conclusions of the workshop are presented in Chapter 6, and the

roadmap towards defining GES for noise is outlined in Chapter 7.


2 Current knowledge gaps

In recent years, it has become increasingly clear that anthropogenic (i.e. manmade) noise can affect

marine life in numerous ways, with the potential for detrimental consequences. These effects can be

broadly categorised as:

acoustic masking of biologically important signals;

behavioural responses;

temporary or permanent auditory impairment, known as Temporary Threshold Shift (TTS)

and Permanent Threshold Shift (PTS);

physiological responses and non-auditory injury, including developmental effects;

in extreme cases, mortality.

It is also evident that there remain significant gaps in our understanding of these effects and of their

consequences. These areas are summarised below, and further details are provided in Annex B.

Themes relevant to all taxa

A broad gap in our current knowledge is how and whether effects on individual animals have

consequences at the population and ecosystem scales. This is the case for all taxonomic groups. To

date, research has largely focused on investigating the effects listed above in individuals or small

groups of animals. However, there is growing recognition of the need to assess how exposure to noise

may ultimately affect population growth rates and ecosystem dynamics, through its effects on

individual fitness and fecundity. A framework for assessing such consequences has been developed

for marine mammals, known as the Population Consequences of Acoustic Disturbance (PCAD) model

(National Research Council, 2005). This framework has also been generalised to include other forms

of disturbance, within the so-called Population Consequences of Disturbance (PCoD) framework.

Further empirical data is needed to derive parameters for this modelling approach for particular

marine mammal species (e.g. New et al., 2013, 2014; Pirotta et al., 2015). It remains to be seen

whether the PCAD/PCoD frameworks are appropriate for other taxa (e.g. fish), and the extent to which

indirect consequences of noise (e.g. on predator or prey species) can be accounted for within them.

Adopting a population consequences perspective leads to a greater focus on the less acute effects of

noise exposure. Shipping noise, a relatively low-level noise source, is the most pervasive in the marine


environment (Hildebrand, 2009), and consequently has the greatest potential to impact populations

and ecosystems through the widespread and chronic effects of acoustic masking, behavioural

responses, physiological stress, and developmental effects (Slabbekoorn et al., 2010). It is therefore

important to highlight that the most severe effects of noise exposure, such as permanent hearing loss

or mortality, are likely to be far less significant than the repeated and widespread low-level effects

listed above when considering population-based and ecosystem-based management of underwater

noise pollution.

A related and emerging strand of investigation concerns cumulative effects related to noise exposure.

Effects may be regarded as cumulative in three ways:

1. Accumulation of deleterious responses over time, i.e. the cumulative effects of repeated or

chronic exposure to noise (Wright et al., 2007; Kight and Swaddle, 2011).

2. The exposure of individuals and ecosystems to multiple noise sources, distributed in space

and time. Much previous research has adopted a reductive approach and considered the

effect of only one noise source or type, and studies are needed which consider how multiple

sources of noise pollution could impinge on a study system (e.g. Pine et al., 2014).

3. The effects of noise exposure when combined with non-acoustic stressors. Noise may not be

the only anthropogenic stressor affecting a population or ecosystem (Science Communication

Unit, 2013), and considering noise in isolation from other factors such as habitat loss or effects

on prey may lead to errors in predicting the consequences of noise disturbance on a system.

To facilitate effective management of underwater noise, a priority area is to better understand how

noise might disrupt individuals and populations at key life stages, such as spawning, nursing, mating

or migration. One of the mitigation tools available to regulators of noise-generating activities is to

impose spatiotemporal restrictions based on the behaviour patterns of at-risk species. More

information on the risks of disturbance at key life stages and the possible benefits of mitigation

measures is needed to support these decisions.

There is increasing recognition that animals which do not avoid artificially noisy environments are not

necessarily unaffected by the presence of anthropogenic noise (Bejder et al., 2009). Animals may

make trade-offs between noise exposure and foraging or mating opportunities, for instance, resulting

in harmful effects without overt behavioural responses. One example is offshore wind farms, which

can act as artificial reefs, creating foraging opportunities for predators (Inger et al., 2009) while also

generating relatively low levels of noise when in operation (Tougaard et al., 2009). A recent study


reported that harbour seals were foraging around these structures for sustained periods, potentially

leading to harmful levels of noise exposure (Russell et al., 2014). Further work is needed to investigate

whether such tolerance of anthropogenic noise exposure may belie detrimental consequences for

exposed animals.

A final theme applicable to all taxonomic groups is the extent to which the results of laboratory

experiments can be extrapolated to freely moving animals in their natural environment. Lab-based

studies have the advantage of a controlled environment, enabling repeated measurements and

control of contextual factors that may otherwise affect responses. However, these conditions are

unrepresentative of the natural environment where the behavioural context may play a key role in

animal responses to noise (Ellison et al., 2012), and the sound fields generated in tank experiments

are likely to be unrepresentative of field conditions (Parvulescu, 1967). On the other hand, in field

studies, it is much more challenging to control experimental variables, and there may be factors other

than noise exposure that elicit responses, leading to misinterpretation of results or the obfuscation of

significant effects. For these reasons, studies are needed which address the linkage between

laboratory and field experiments, such as by scaling up controlled experiments into the field (e.g. using

mesocosms or large, contained water bodies) to provide an intermediate scale of assessment, or by

developing methods to corroborate the findings of lab-based studies in the field.

Themes specific to fish and invertebrates

Over the last two decades, much of the research into the effects of noise on marine life has

concentrated on marine mammals. However, in recent years, the number of studies on fish and

invertebrates has grown rapidly, leading to greater understanding of the effects of noise on lower

trophic levels and possible consequences for ecosystem dynamics. A key constraint on acoustic studies

of fish and invertebrates is that these taxa primarily sense sound through the particle motion

component of the sound field (Popper and Fay, 2011; Morley et al., 2014). The conventional means of

measuring sound underwater is by measuring sound pressure (another component of the sound field)

using hydrophones, but for most environments it is not possible to use this to derive the particle

motion. Commercial devices to measure particle motion are becoming available, but research into

applying these in field measurements is still in its infancy (Merchant et al., 2015). Field studies are

needed to quantify particle motion from sound sources and to examine associated responses of fish

and invertebrates to this component of the sound field.


A greater understanding of the hearing sensitivities of fish and invertebrates is also required,

particularly in relation to particle motion (Popper and Fay, 2011). This will require the development

of devices and protocols to make such measurements for particle motion (Popper et al., 2014).

On the whole, little is known about the impacts of anthropogenic underwater sound exposure on

marine invertebrates (Normandeau Associates, 2012), though several studies have reported adverse

behavioural and physiological effects (e.g. Wale et al., 2013a, 2013b; Filiciotto et al., 2014).

‘Invertebrates’ covers a wide range of organisms and the range of responses to noise in this group

may be correspondingly diverse. To prioritise research needs, it may be beneficial to focus on species

with high ecological or socio-economic importance.

With regard to eggs and larvae of fish and invertebrates, information on sound levels at which lethal

and sub-lethal effects occur is very limited (but see, e.g. Bolle et al., 2012; de Soto et al., 2013; Nedelec

et al., 2014). Further research is needed into these effects, including behavioural responses and

developmental consequences.


3 Legislation review

Regulation and enforcement vary greatly among jurisdictions, and a range of national and

international laws and guidelines are currently in place. Before summarising these noise management

instruments, it is worth briefly considering the available means of mitigating the effects of underwater

noise pollution. These measures can be divided into four broad categories:

1. Location and timing. Spatiotemporal management of noise-generating activities to avoid

habitats and periods with a greater vulnerability to noise pollution.

2. Mitigation equipment. Physical barriers to reduce noise radiated from activities (e.g. bubble

curtains for pile driving operations) and devices to displace marine fauna to reduce risk of high

noise exposures (e.g. acoustic deterrent devices (ADDs) or use of ‘ramp-up’ at onset of

operation).

3. Source quieting. Use of alternative methods with lower noise emission (e.g. vibration piling

rather than impact piling) or modifications to existing noise sources to reduce noise output

(e.g. ship quieting technologies).

4. Real-time mitigation. Delay or interruption to noise generating activities based on

observations of at-risk species in the vicinity (e.g. marine mammal sightings or passive acoustic

detections).

Effective management of underwater noise pollution will require a combination of these measures

spanning local, national, regional, and global jurisdictions to address the variety of scales at which

noise generating activities are regulated. For example, shipping routinely traverses international

boundaries and so will require a coordinated international approach. Offshore construction projects

may introduce significant levels of noise across national boundaries and so demand a bilateral or

regional approach to managing cumulative effects. Some activities may be sufficiently localised that

they can be managed at a local or national level. In the following summary, existing management

instruments to address noise pollution are briefly reviewed; further details are provided in Annex A.

At a global level, the United Nations Convention on the Law of the Sea (UNCLOS) defines pollution as

“the introduction by man, directly or indirectly, of substances or energy into the marine environment,

including estuaries, which results or is likely to result in such deleterious effects as harm to living

resources and marine life...” (UNCLOS, 1982). This can be interpreted as encompassing noise, but this

view has not been officially adopted by UNCLOS. In 2014, another UN body - the International

Maritime Organization (IMO) - adopted non-mandatory guidelines in relation to shipping noise (MEPC


66/17). These guidelines set out a ten-point work plan to address current knowledge gaps in ocean

noise (see Annex A), although these proposals are non-binding.

Within Europe, a range of multinational and EU-wide agreements are in place. The Marine Strategy

Framework Directive (MSFD) addresses underwater noise directly under Descriptor 11. Two Indicators

within this Descriptor describe impulsive sound (11.1.1) and ambient sound (11.2.1). The MSFD aims

to achieve GES (Good Environmental Status) for European seas, with a recurring six-year assessment

cycle. Targets for these Indicators have yet to be developed, and the definition of GES with respect to

noise remains qualitative: “input of energy, including underwater noise, is at levels that do not

adversely affect the marine environment.” Prior to the MSFD, a number of other Directives (e.g.

Environmental Impact Assessment, Strategic Environmental Assessment, Habitats and Species) were

used to address underwater noise issues, and remain relevant in their respective areas.

A number of European bodies (e.g. OSPAR, HELCOM) provide fora for regional cooperation among

nations with shared seas, including with regard to MSFD Descriptor 11 implementation. Two non-

binding multilateral agreements to promote the conservation of cetacean species have also addressed

underwater noise issues. The Agreement on the Conservation of Cetaceans of the Black Sea,

Mediterranean Sea and Contiguous Atlantic Area (ACCOBAMS) was signed by 23 countries bordering

these waters, while the Agreement on the Conservation of Small Cetaceans of the Baltic, North East

Atlantic, Irish and North Seas (ASCOBANS) is a similar coordination tool for the named region. These

Agreements call on participating countries to address underwater noise pollution with regard to

cetacean conservation, although there is no provision for the legal enforcement of these

recommendations.

At a national level, several countries have introduced mandatory requirements in relation to

underwater noise pollution. One example is Germany, where a threshold for pile driving noise has

been implemented: the peak-to-peak sound pressure level from piling must not exceed 190 dB re 1

µPa outside a 750 m perimeter from the pile. In other countries, legislation to protect certain species

has been used to impose restrictions on noise generating activities. For example, in the United States

marine mammals are given protection from injury and behavioural disturbance under the Endangered

Species Act and the Marine Mammal Protection Act. The requirements of these statutes have formed

the basis for developing sound exposure thresholds for these species.

Finally, a number of countries have adopted guidelines for mitigating the effects of certain noise

generating activities. In the United Kingdom, the Joint Nature Conservation Committee (JNCC) has

developed marine mammal mitigation guidelines for seismic surveys, marine explosives, and marine


piling (e.g. JNCC, 2010). In each case, a mitigation zone to be surveyed by marine mammal observers

(MMOs) is defined (within a specified distance from the activity), and procedures for beginning

operations with a soft start (ramp-up) are outlined. Another example is New Zealand, where a code

of conduct has been developed for seismic surveys to mitigate the potential effects on marine

mammals (New Zealand Department of Conservation, 2013). Similarly to the JNCC guidelines, these

specify mitigation zones and soft start procedures for seismic operations.


4 Review of underwater acoustic propagation models

A number of ‘off-the-shelf’ acoustic propagation modelling solutions have been developed, and are

widely used in the underwater acoustics community. These models apply particular solutions to the

wave equation, and can be downloaded from open sources (e.g. http://oalib.hlsresearch.com/). No

single model provides an efficient and applicable solution to all scenarios: each has advantages and

disadvantages in relation to their suitable frequency range, water depth, computational requirements

and ability to account for spatial variability in the environment (Jensen et al., 2011). Table 1

summarises some of these factors for five commonly used models; further details are provided in

Annex E.

Table 1. Suitability of five commonly used propagation models for different water depths and frequencies (see

Annex E for details).

It is critical to select an appropriate model for a particular scenario, yet even a suitable model can only

be predictive if the input data are accurate and of a sufficient spatial and temporal resolution. Indeed,

the quality of input data is typically the key constraining factor in underwater propagation modelling,

since gathering marine environmental data is costly and existing datasets (typically collected for other

purposes, e.g. geophysical surveys) may not be adequate. The relevant parameters can include, for

example, bathymetry, seabed data, sound speed profile, and sea surface roughness. The seabed

properties in particular are a key factor in modelling propagation in the shallow, continental shelf

waters that are typical of several European seas. For large-scale applications such as sound maps,

Shallow water - low frequency

Shallow water - high frequency

Deep water - low frequency

Deep water - high frequency

Ray theory Ray theory Ray theory Ray theory

Normal mode Normal mode Normal mode Normal mode

Wave number integration




Parabolic equation Parabolic equation Parabolic equation Parabolic equation

Energy flux Energy flux Energy flux Energy flux

Green – suitable; Amber – suitable with limitations; Red – not suitable or applicable

http://oalib.hlsresearch.com/


small changes or errors in these input parameters could have a considerable effect on model

predictions, and so it is important that field measurements are undertaken to validate results and to

help to identify sources of uncertainty. Such corroboration is the only reliable way to verify that model

predictions are accurate. The more a model has been benchmarked in this way, the more confidence

there can be in extrapolations into similar environments that are lacking validation measurements.


5 Use of sound maps for assessing Indicator 11.2.1

It has been suggested that a combination of measurements and modelling will be required to evaluate

Indicator 11.2.1 of the MSFD (Dekeling et al., 2014). Deploying acoustic monitoring equipment at sea

is costly, and providing adequate spatial resolution across EU waters using only measurements would

be prohibitively expensive and logistically challenging. This difficulty can be overcome through the use

of acoustic propagation models, which extrapolate from measurements based on environmental

parameters and sound source characteristics as described in the previous chapter. Models based on

the spatial distribution of sound sources can be used to produce maps of sound levels at large spatial

scales (e.g. Erbe et al., 2012; Heaney, 2014). Such sound maps need to be ground-truthed and

optimised using calibrated measurements of sound levels if they are to produce valid results

(Merchant et al., 2015).

The validation of modelling to produce sound maps is an iterative process, as there are a variety of

parameters which can affect the model predictions. These include the accuracy of the propagation

modelling used (which in turn depends on the quality of environmental input data, such as seabed

properties) and of the sound levels assumed to be generated by the noise sources. As part of this

project (see Annex F), a four-step framework (roadmap) was developed for producing validated sound

maps:

1) A priori modelling. Before undertaking a noise monitoring programme, a priori modelling can

be used to identify sites at which measurements will most reduce uncertainty in the model,

allowing an efficient use of resources.

2) Initial validation measurements. Having identified suitable monitoring sites in Step 1, initial

monitoring at these sites can be undertaken to quantify the degree of agreement between

the a priori model and the initial measurements.

3) Iterative optimisation. To improve the model predictions, the next stage is then a feedback

loop in which the greatest sources of error or uncertainty in the model are identified and

reduced in each iteration. Reducing these errors will involve improving the quality of the

model input parameters, and possibly altering the modelling approach itself. Better input data

may be obtained by making targeted measurements, such as of ship source levels,

environmental parameters, or propagation loss.

4) Mature results for Indicator 11.2.1. The validated output is then a two-dimensional depth-

averaged map of the Indicator over the relevant marine region.


In practice, the site selection for field measurements will also be influenced by practical considerations

such as the costs of deployment and whether pre-existing monitoring stations can be utilised.

Figure 1: Shipping sound map of unweighted SPL [dB re 1 μPa] in the 1/3-octave band centred at 125 Hz

(Annex F). Green border indicates the land boundary and white border the Exclusive Economic Zone (EEZ) of

the Netherlands. X and Y axes indicate longitude and latitude, respectively.

Sound maps were produced for two areas in EU waters for the purposes of this project: the

Netherlands EEZ and a site between Madeira and the Canary Islands (see Annex F for details). Figure

1 shows an example for the Netherlands EEZ for the 125 Hz band based on AIS shipping data, and is

an example of a priori modelling for Step 1 of the sound mapping framework. To produce validated

sound maps, field measurements at comparable spatial and temporal scales are needed which will

help to identify sources of error and refine the model parameters as outlined above.

A number of different developers and research groups are developing tools to create sound maps, and

it will take time before these techniques are sufficiently mature and standardised to be implemented

in a policy context. Variability in mapping predictions will result from differences in modelling

approaches among Member States, and it is important that GES assessment is not dependent upon

the particular modelling approach chosen. In addition to an agreed modelling benchmark for sound

mapping, consistency is needed in the input data, including: AIS ship-tracking data; estimates of noise

source levels; and environmental data (e.g. seabed properties, bathymetry, meteorological data,

water column properties).


6 Outcomes of workshop on methodologies and guidelines

As part of the project, a workshop entitled Propose methodologies and guidelines on how to evaluate

impacts of noise on marine biota was convened in Brussels on 10-11 April 2014 (see Annex C for full

details). The workshop was co-chaired by Mark Tasker (JNCC) and Fabrizio Borsani (CEFAS), and was

attended by 37 delegates from industry, academia, NGOs, and DG Environment. Five international

experts provided insight into particular areas, specifically: the effects of noise on invertebrates (Michel

André), fish (Michele Halvorsen), and marine mammals (Christine Erbe); the PCAD (Population

Consequences of Acoustic Disturbance) framework (John Harwood); and noise modelling and mapping

(Kevin Heaney).

The aims of the workshop were to:

a) Discuss and propose a roadmap towards defining Good Environmental Status (GES) for

underwater noise;

b) Identify knowledge gaps and define research needs to address the impacts of underwater

noise on marine biota;

c) Provide guidance for important features and considerations that a proposal related to the

effects of underwater noise should have when submitted to the EC for funding.

The principal conclusion of the workshop was that there is currently insufficient knowledge to define

GES in relation to underwater noise or to set quantitative and evidence-based targets. To make

progress towards achieving these goals, key knowledge gaps should be addressed.

The following were identified as priority knowledge gaps and/or needs for future action:

1. The current understanding of the adverse effects of sound on the marine ecosystem and

marine fauna is limited. The main areas of concern are related to long-term effects of elevated

ambient noise levels at the population and ecosystem scales. Assessment of these effects

could be based on observations and modelling at the levels of populations, food webs and

ecosystems. Another major gap is the lack of data on the particle motion component of

underwater noise, which is the principal means by which fish and invertebrates detect sound.

Primary research into the effects of noise on these groups in relation to particle motion will

be critical to understanding potential risk. Finally, there is a need to better understand the

limitations and opportunities in extrapolating the results of controlled lab-based experiments

to populations in their natural environment. One way of evaluating the validity of such


extrapolations is to conduct controlled field experiments to provide an intermediate scale of

assessment.

2. Underwater noise monitoring is needed to support the implementation of the Marine

Strategy Framework Directive. While no international standards are available for underwater

noise monitoring, standards developed by Member States such as those developed by the

BIAS project in the Baltic Sea may be adopted or adapted for wider application to EU waters.

It is important that monitoring is carried out in a standardized way, so that the results can be

displayed, evaluated and compared consistently across Member States.

3. There is a need to identify or develop cost-efficient monitoring tools to monitor ambient

sound at relevant frequencies to obtain the data needed to address Descriptor 11. A common

EU-wide approach to the development of sensors and monitoring tools is desirable to avoid

duplication and to harmonize approaches.

4. To better define GES for noise and its relations to other Descriptors, further work and

guidance are needed. The introduction of thresholds or single-number levels appears

questionable from an ecological standpoint, but is practicable and fits within the

environmental monitoring paradigm of the MSFD. Indicators and targets should therefore be

carefully evaluated, taking into consideration their practical implementation as management

tools as well as advances in the available scientific evidence. There is also uncertainty over

whether setting uniform thresholds for underwater noise across European seas is a

reasonable approach, and whether noise should also be evaluated in concert with other major

stressors to give an indication of the cumulative pressure that these ecosystems sustain.

The final aim of the workshop was to provide guidance on important features for funding proposals

to the EC on the effects of underwater noise on marine biota. An extensive list of suggestions was put

forward (see Annex C for details), including:

Highlighting socioeconomic value, stakeholder engagement, impact on policy and/or enabling

GES assessment.

Providing publicly available datasets to allow open analysis of results for future work.

Transparent assessment of uncertainties, errors, and biases in the methods and results.

Clear documentation of environmental and contextual factors which may affect the results.

Use of openly available, peer-reviewed techniques (e.g. in noise modelling) to ensure

transparency and repeatability.


7 Roadmap

This final chapter considers the way forward to define GES for underwater noise. In previous chapters,

key knowledge gaps were identified and the obstacles to defining GES were discussed in detail. Here,

a number of concrete steps are proposed to reduce uncertainty in the evidence base and to make

progress towards defining effective GES criteria for underwater noise.

It is important to recognise at the outset that MSFD Descriptor 11 is the first legislative instrument to

address ecosystem-based management of underwater noise pollution in a quantitative manner. The

EU is leading the way in developing quantitative, practicable, evidence-based targets to ensure that

underwater noise does not adversely affect the marine environment. This process of developing

targets for Descriptor 11 remains a work in progress, and has involved extensive consultation with the

scientific community, including through the Technical Group on Underwater Noise (TG Noise).

Achieving this goal will mean aligning GES criteria with the best available scientific evidence while also

ensuring that GES can be readily translated into operational targets for regulators of noise generating

activities.

There follows a number of proposed Actions informed by the outcomes of the previous chapters.

Indicative costs and timeframes have been associated with each Action. There are a range of

organisations that could undertake the work described. In some cases, such as standard setting,

certain international bodies may be appropriate. In others, where a number of groups could

potentially undertake the work, it is recommended that an open public tender process be

undertaken. To ensure that such calls for tender reach all parts of Europe, international bodies such

as OSPAR, HELCOM, Barcelona and Black Sea Conventions, and ICES should be asked to help in

advertising the calls. Funding for some of these actions may be found within the current LIFE+

framework, as well as within future HORIZON 2020 calls. New INTERREG calls may be relevant to

Action 3 at the regional level, since they involve small and medium-sized enterprises (SMEs) to provide

a technical component and local regulatory bodies to put monitoring in place.

Action 1: Agree standards for underwater noise monitoring (2015-2016)

A variety of metrics and terminology are in use across the EU to describe underwater sound.

Depending upon their technical background, scientists, developers, and military operators carry out

measurements and analysis in different ways. To assess Descriptor 11 consistently across the EU,

standards are needed for data acquisition, analysis, and modelling, that can be applied in all EU waters.

While it would be convenient to adopt a suitable international standard (e.g. International


Organization for Standardization (ISO) standard), no such standards for ambient noise monitoring or

mapping exist. International standards may be developed in the future, but the timescale is likely to

be at least six years (see Annex F), and it is not clear that such standards will necessarily be aligned

with the MSFD policy objective of attaining GES. For these reasons, it is incumbent upon Member

States to agree EU-wide standards for MSFD implementation.

Considerable progress has already been made by the EC-funded BIAS project, which has developed

standards for data handling and sensors (Verfuß et al., 2014), and plans to publish standards for signal

processing. These standards were developed for use in the Baltic Sea, but could be adopted or adapted

for use throughout EU waters. In addition to measurement standards, standards for modelling and

mapping of underwater sound for Indicator 11.2.1 are needed. Since sound maps are in a relatively

early stage of development, and the key priority for Indicator 11.2.1 assessment is to begin monitoring

(Dekeling et al., 2014), the focus of standardisation initially should be to agree measurement and

analysis standards. To this end, TG Noise should consider, in consultation with international experts,

how the BIAS standards can be adapted for application throughout EU waters, leading to an

operational standard for measurement and analysis endorsed by TG Noise. Subsequent workshops

can then explore how sound maps can be validated and standardised as these techniques become

more mature.

This Action can be achieved through a series of workshops, under the aegis of the ongoing TG Noise

work programme. These workshops would bring together international (i.e. including non-EU)

specialists, so costs would comprise travel and subsistence for those specialists and some local venue

costs. An estimated timeframe of 1-2 years would be required to agree and refine the measurement

and analysis standards.

Sound mapping standards may be premature at this stage since these techniques have yet to be

extensively validated and optimised with field measurements. Nevertheless, knowledge exchange and

benchmarking of sound mapping methods is needed to promote consistency, and progress towards

validated sound maps will accelerate as field data from MSFD noise monitoring programmes become

available. A series of workshops should be convened to share the latest developments in sound

mapping and to work towards standardisation among Member States.

Costs for these workshops are anticipated to be approximately €50,000 per year.

Action 2: Commission studies to address key knowledge gaps (2015-2018)

Targeted studies are needed to address key knowledge gaps in our understanding of the effects of

noise on marine ecosystems. Uncertainties over the effects of underwater noise on marine fauna


currently constrain management decisions and hinder progress towards defining GES. A detailed

summary of the key topics was provided in Chapter 2, and topics emerging from the workshop were

outlined in Chapter 6. Common themes include (but are not limited to) the need for greater

understanding of the population and ecosystem consequences of noise exposure, the need to assess

the particle motion component of the sound field in relation to fish and invertebrates, and a need to

more fully understand the limitations and opportunities in extrapolating experimental results to wild

animals.

Research to address these issues can be commissioned under various EU funding mechanisms (e.g.

HORIZON 2020, Life+, INTERREG), and will require a concerted and coordinated effort to direct funding

at projects which will reduce uncertainty in environmental assessment. An indicative timeframe to

achieve results from these projects is 4 years. Costs for the work may be in the region of €5-10 Million,

and are high due to the anticipated need for extensive field work and novel instrumentation.

Action 3: Agree common standards for noise monitoring instruments (2015-2018)

Further to the standardisation in monitoring techniques identified in Action 1, there is also a need to

standardise the sensor technology used to monitor underwater sound. A variety of devices are

commercially available, and some may not be adequate to meet the requirements of noise monitoring

for the MSFD. Work to establish standards and guidelines for suitable monitoring technologies could

fall under Action 1. Another option is to develop appropriate and cost-effective monitoring equipment

that could be deployed across EU waters to ensure standardised results for GES assessment. This

coordinated approach would help to avoid duplication in sensor development, and could be achieved

through collaboration between Member States and industry, academia, and researchers. Initial efforts

are already underway within the EU-funded Common Sense project

(http://www.commonsenseproject.eu/), and further development will be required to produce a fully

operational system. The initial timeframe for this Action is estimated to be 4 years, with potential

development costs of up to €6 Million.

Action 4: Define operational GES criteria (2016-2017)

It is clear that there is currently insufficient scientific evidence to support a comprehensive assessment

of the levels at which anthropogenic noise may adversely affect the marine environment. Indeed,

there will always be uncertainty over what levels of impulsive and ambient noise may lead to adverse

effects. Nevertheless, this uncertainty need not preclude the development of Indicators and targets

to attain GES based on the best available scientific evidence. A combination of scientific data and

expert judgement will be required to define GES in a way that is proportionate to the risks and

http://www.commonsenseproject.eu/


uncertainties involved and in a form that can be implemented as an operational management tool. It

is important to note that this situation is not unprecedented. For example, in relation to the effects of

noise on marine life, noise exposure thresholds have been developed for marine mammals (Southall

et al., 2007) and fish (Popper et al., 2014) despite considerable knowledge gaps and uncertainties in

the available scientific evidence. Making progress towards defining GES for noise will require an

understanding from the scientific community that operational targets are needed that can be

implemented as policy. If necessary, these targets can be refined in subsequent assessment cycles as

more information becomes available.

The two Indicators within Descriptor 11 are complementary and address two aspects of the effects of

underwater noise. In defining GES for noise, care should be taken to ensure that the Indicators and

targets remain complementary and are relevant to the consequences of noise exposure for marine

fauna. Indicator 11.1.1 addresses impulsive noise, which has been linked to injury, displacement, and

disturbance. Indicator 11.2.1 addresses ambient noise: increasing ambient noise levels have the

potential to mask acoustic cues, raise stress levels, and have developmental and behavioural effects.

The noise sources that the Indicators address are similarly distinct and require different management

strategies: the primary sources of impulsive noise are pile driving, seismic surveys, and explosions,

which are all discrete events in space and time, while the main contributor to rising ambient noise is

shipping, which is continuous and widespread throughout the marine environment.

Taking each Indicator in turn, the main challenges in defining GES will be outlined, and then an Action

plan to resolve the remaining issues will be put forward.

Indicator 11.1.1 (low and mid-frequency impulsive sounds) is currently defined as (Dekeling et al.,

2014):

The proportion of days and their distribution within a calendar year, over geographical

locations whose shape and area are to be determined, and their spatial distribution in which

source level or suitable proxy of anthropogenic sound sources, measured over the frequency

band 10 Hz to 10 kHz, exceeds a value that is likely to entail significant impact on marine

animals.

Source level thresholds for inclusion of particular noise sources in Indicator 11.1.1 (i.e. those that are

likely to entail significant impact) have already been proposed by TG Noise (Dekeling et al., 2014). The

remaining questions to be resolved in defining GES with respect to impulsive noise can then be

summarised as:


1. What is an appropriate EU-wide spatial scale to evaluate Indicator 11.1.1? In defining a

spatial resolution, consideration should primarily be given to the relevance to potential effects

on marine life, and secondarily to factors such as existing assessment areas (e.g. licensing

blocks), which may differ between Member States.

2. How can a target for GES be formulated based on this Indicator? Indicator 11.1.1 has both

spatial and temporal dimensions, and a GES target must similarly address both aspects;

guidance could be sought from other areas of environmental science and policy which may

have developed analogous targets.

Indicator 11.2.1 (ambient noise) is currently defined as (Dekeling et al., 2014):

Trends in the annual average of the squared sound pressure associated with ambient noise in

each of two third octave bands, one centred at 63 Hz and the other at 125 Hz, expressed as a

level in decibels, in units of dB re 1 μPa, either measured directly at observation stations, or

inferred from a model used to interpolate between or extrapolate from measurements at

observation stations.

There are several outstanding questions to be resolved before this Indicator can be applied to GES

assessment. These include:

1. What is a suitable metric to track trends in ambient noise levels? The current TG Noise

guidance is to use the arithmetic mean (Dekeling et al., 2014), but this metric is strongly

dominated by the loudest noise levels (Merchant et al., 2012). This means that in many areas

impulsive noise may skew this Indicator away from the overall trend in background noise,

confounding assessment of whether ambient noise levels overall are rising or falling, or have

exceeded a certain threshold. To reflect general trends in ambient noise - which are linked to

levels of acoustic masking and noise-induced stress - an Indicator based on percentiles of the

ambient noise level distribution may be more representative and relevant, as has been applied

in studies of acoustic masking (e.g. Clark et al., 2009; Hatch et al., 2012).

2. What is an appropriate target for Indicator 11.2.1? Similarly to Indicator 11.1.1, levels of

ambient noise have both a spatial and temporal aspect. Spatial variation in ambient noise

levels may be modelled using sound maps, but these techniques are still in development, and

it is important that attainment of GES does not depend upon the particular modelling

approach employed by a Member State. Until sound mapping methods are well established

and validated, measurements should constitute the primary means of GES assessment. The

question is then how to formulate a suitable ambient noise target. Setting an absolute


threshold above which GES is not attained may seem arbitrary given the uncertainty in the

relationship between pressure, status and impact. One alternative strategy could be to use

expert judgement to derive a threshold above which ambient noise levels are probable to

cause adverse effects, and then stipulate a minimum proportion of time that noise levels

should fall below this threshold to attain GES.

Reaching sufficient consensus on these issues to enable an operational definition of GES will be

challenging, but can be achieved if targeted efforts are made to resolve the aspects that depend on

expert judgement. This work could progress through a series of workshops with agenda items focused

on resolving the outstanding issues. These workshops should draw on a broad pool of international

expertise, and should seek the involvement of experts with previous experience of formulating noise

exposure thresholds, as well as those with experience of environmental management of

anthropogenic noise. The timeframe would be set initially to two years, with a potential for reiteration

at the end of every 6-year MSFD cycle. Costs may be in the range of €50,000-100,000 per year,

depending upon how much overlap there is with planned TG Noise activities.


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